#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(void)
{
    if(setvbuf(stdout, NULL, _IONBF, 0)){
        perror("setvbuf error");
        exit(0);
    }

    printf("Hello World!\n");
    printf("Hello World!");

    for (;;)
        sleep(1);
}   
